1. Field of the Invention
The present invention relates to a cut sheet feeding device having a function of detecting a skew of the sheet to be fed. In particular, the present invention relates to a cut sheet feeding device capable of detecting a skew of the document of standard size to be read by an image scanner having a mechanism for feeding the document, or a skew of the blank form to be printed by a printer having a mechanism for feeding the form.
2. Description of the Related Art
Computers are widely used in offices and homes to print texts on a blank form with a printer, or read an image from printed matter with an image scanner and store the image. The form to be printed by printer or the document to be read by image scanner must have no skew in a sheet feeding direction.
To read an image without skew from a document by image scanner, it is necessary to detect a skew of the document and correct it before feeding and reading the document.
If the blank form to be printed has a skew, print on the form will be skewed to provide a bad appearance.
Various cut sheet feeding devices capable of detecting a skew of the document to be fed have been proposed. In the following explanation, a blank form printed by printer or printed matter read by scanner is referred to as a document.
Some image scanners read data from a document while feeding the document. These image scanners have size sensors for detecting the size of the document fed. The size sensors detect, for example, document sizes B5, A4, B3, and A3, respectively. The size of a document is determined by checking which sensors the document has covered.
In addition to the size sensors, the image scanner usually has two document sensors for detecting the feeding state of a document. The document sensors are arranged along a document feeding path, to determine whether or not the leading edge of the document is moving correctly. For example, one of the document sensors is used to determine whether or not the document is moving correctly, and the other to determine the timing for reading the document.
The operator of the image scanner sets the size of a document to be read, and the document is fed into the image scanner. The size sensors and document sensors provide outputs to indicate whether or not they have detected the document. The outputs of the sensors are transferred to a computer connected to the image scanner, and the computer detects a skew of the document according to the outputs.
The skew detected by the computer is displayed on a display. The displayed skew involves a skew in a main scanning direction, i.e., a gap between the left and right ends of the leading edge of the document and a skew in a secondary scanning direction, i.e., a gap between the front and rear ends of the left edge of the document.
According to the prior art, the operator must check the gaps in the main and secondary scanning directions of every document on the display to determine whether or not the document is skewed. This is laborious for the operator.
Recent image scanners operate at high speed, and therefore, it is very difficult for the operator to check the skew of each document on the display. Even if the operator finds a skew on a given document, it is nearly impossible for the operator to quickly carry out an error correction process.